With the passage of time it is not uncommon for electrical boxes to become loose from the structures they are mounted to. Frequent attachments of plugs into an electrical outlet over time, for example, can cause the supporting outlet box to become unattached from the structure. The loosened electrical box is then a hazard, as it can cause loosening of wires within the box, electrical shorts, and potentially electrical shocks.
When an electrical box becomes loose, a prime consideration in replacing the box is minimizing damage to the surface surrounding the box. Electrical boxes for interior walls therefore must be capable of being easily installed into and secured to the existing wall without causing damage to the surrounding wall surface.
Electrical boxes have been developed specifically for the replacement of old electrical boxes, which are typically referred to as “old work” boxes. Prior art boxes of this type are described in U.S. Pat. No. 4,297,525 to Bowden, Jr., U.S. Pat. No. 4,120,473 to Suk, U.S. Pat. No. 5,603,424 to Bordwell et al., and U.S. Pat. No. 5,600,093 to Herth et al. In the above patent to Bowden, Jr., a box is shown which employs threaded mounting screws fastened into pawl arms. The pawl arms include tabs extending therefrom. After the box is inserted in an opening in a wall, tightening on the mounting screws urges the tabs linearly toward the box and eventually secures the box to the wall. Suk discloses a box that works in conjunction with a bracket to tighten against the wall. Bordwell et al. discloses a mounting assembly that includes clip-on securement members that are mountable to the outer sidewalls of an electrical box. Each securement member includes a bracket positioned on an external surface of the sidewall and a brace supported by the bracket. The brace is movable on the bracket so as to clamp the box to the mounting wall. Herth et al. discloses a modular interchangeable electrical work box. The work boxes have insert sheaths for fasteners for attaching the work box to a stud.
Although the patents to Bowden, Jr., Suk, and Bordwell et al. disclose electrical boxes for use in old work situations, they all rely on clamping type mechanisms that tighten onto the wall covering of the structure. Unfortunately, the wall covering is typically not a structurally strong portion of the wall. Sheet rock for example is used on interior walls, and is not a high strength material. So although the electrical boxes may clamp onto the wall material, the resulting electrical box is not very strongly attached.
The electrical box disclosed in Herth et al. improves the installation by providing fastener insert sheaths and fasteners. The fasteners are driven into the studs of the wall instead of into the wall covering. Although this is an improvement over the prior art boxes that employ clamping members, as a result of providing the fastener insert sheaths, the one piece box disclosed by Herth et al. loses a large portion of the internal volume of the box. Therefore, although the box provides a better connection to the wall, the resulting volume within the box is small and provides inadequate space for completing wiring connections within the box.
What is needed therefore is an electrical box that can be securely fastened to a structurally strong portion of the wall while at the same time providing adequate internal volume for completion of all wiring connections.